Gold has many important industrial applications including production of jewelry and production of electronic circuits, electrical contact surfaces, and components. In recent years, industrial use of gold has become increasingly important. There are several reasons for this increased use and importance of gold. First of all, gold does not form a surface insulating film such as a gold oxide film. For this reason, gold has a high surface luster which is quite attractive when used in jewelry articles. For the same reason, its use in electrical circuits and components is highly desirable because surface contact to gold usually exhibits low electrical resistance.
Gold also has the advantage of being chemically inert. The use of gold often increases the lifetime and reliability of devices and articles since gold is not affected by many chemicals or adverse conditions of temperature and humidity. A particular case in point is the production of integrated electronic circuits. Here quite thin and narrow conducting paths are required. Many metals (i.e., copper) might be satisfactory as far as electrical conductivity is concerned, but they rapidly degrade with time. Gold has the advantage of being inert, and also exhibits quite high electrical conductivity.
Because of its excellent electrical contact properties, gold is often used in electrical connectors, switches and relays. By the addition of small amounts of various elements (for example, arsenic, cobalt, nickel), gold can be made quite hard and resistant to abrasion. The particular procedure for hardening the gold depends on the process for producing the gold surface. For example, certain applications might invole an electroplating procedure and another an inlay or evaporation procedure. Various procedures are outlined in a book entitled, Gold Usage by W. S. Rapson and T. Groenewald, Academic Press, New York, 1978.